JP5391978B2 - Fluid holding device - Google Patents

Description

  The present invention relates to suppression of a reduction in guiding accuracy due to a disturbance load of a fluid holding device such as a static pressure bearing or a static pressure guide.

  As a technology for suppressing a decrease in bearing accuracy due to a disturbance load applied to a hydrostatic bearing, a conventional technology for controlling a supply pressure to a fluid bearing according to a displacement due to a disturbance load on the main shaft and suppressing a decrease in accuracy (see, for example, Patent Document 1) In addition, there is a conventional technique (for example, see Patent Document 2) that controls the supply pressure to the fluid bearing in accordance with the pocket pressure fluctuation due to the disturbance load on the main shaft to suppress the accuracy reduction.

In the case of the prior art described in Patent Document 1, specifically, in FIG. 4, the main shaft 3 is a hydrostatic bearing in which pressure oil held at a predetermined pressure by a pump 13 and a pressure control valve 14 is supplied via a throttle. 16 and 17 are rotatably supported by the main shaft rotating motor 15, and the relative displacement between the static pressure bearings 16 and 17 and the main shaft 3 is measured by the displacement sensors 9 and 10.
In the static pressure bearing configured as described above, the principle of suppressing the decrease in accuracy is as follows.
When the machining force during steady machining is F, the displacement of the main shaft 3 is E, the bearing stiffness is K, the disturbance force is ΔF, and the displacement increase amount of the main shaft 3 to which the disturbance force is applied is ΔE, E = F / K, E + ΔE = (F + ΔF) / K is established. Here, if the main shaft rigidity is increased by ΔK and E = (F + ΔF) / (K + ΔK) is established, the displacement amount of the main shaft 3 does not change even when the disturbance force ΔF is applied, so that the main shaft rotation accuracy (bearing accuracy) decreases. do not do. Since the rigidity of the hydrostatic bearing is proportional to the supply pressure, assuming that the initial supply pressure is P and the increased supply pressure is ΔP, (K + ΔK) = K (P + ΔP) / P and ΔK = K · ΔP / P is established. From E = (F + ΔF) / (K + ΔK), ΔK = ΔF / E, and ΔF = K · ΔE, so ΔK = K · ΔE / E holds. Therefore, K · ΔP / P = K · ΔE / E, and the increased supply pressure ΔP becomes ΔP = P · ΔE / E.
From the above, in order to eliminate the increase in displacement of the main shaft 3 due to the disturbance force ΔF, the supply pressure may be increased by ΔP = P · ΔE / E.
A specific action that suppresses a decrease in bearing accuracy due to a disturbance load will be described below.
Based on the displacement increase amount ΔE measured by the displacement sensors 9, 10, the control device 18 increases the increased supply pressure ΔP that becomes bearing rigidity necessary to push back the main shaft to the standard displacement position at the time of steady machining from ΔP = P · ΔE / E. Calculate and command the pressure control valve 14. When the pressure control valve 14 supplies pressure oil whose pressure has been increased by ΔP to the bearings 16 and 17, the rigidity of the bearings 16 and 17 is increased, and the displacement of the main shaft 3 due to the disturbance force is reduced. By continuously performing the above control, a decrease in bearing accuracy due to disturbance force is suppressed.

  In the case of the prior art described in Patent Document 2, at least one of a plurality of throttles of the oil supply pipe line to the static pressure pocket is movably supported, and the terminal end of the supply pipe line is changed according to the fluctuation of the pressure in the pocket due to the disturbance load. Controls the pressure supplied to the throttle to suppress a decrease in bearing accuracy due to disturbance force.

JP 2003-89026 A JP 2002-286037 A

When a disturbance force is applied to the fluid holding device, a displacement determined by the fluid holding device rigidity and the magnitude of the disturbance force is generated, and the fluid holding accuracy is lowered.For example, when used for a spindle device of a machine tool, A decrease in fluid holding accuracy directly leads to a decrease in machining accuracy of the workpiece. In the prior art described in Patent Document 1 and Patent Document 2 described above, the pressure control of the hydrostatic bearing for suppressing the decrease in fluid holding accuracy is performed by controlling the supply pressure to the throttle. There was a limit to the pressure response speed in the pocket, and when the disturbance force fluctuation was high, the response was poor and the deterioration in accuracy could not be suppressed sufficiently.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluid holding device that can suppress a decrease in accuracy due to a disturbance force even with a high-speed disturbance force fluctuation.

  In order to solve the above problems, the invention according to claim 1 is characterized in that a static pressure pocket comprising a recess and a land provided around the recess, and a pressure oil supply means for supplying pressure oil to the recess. A moving body supported by pressure oil in the static pressure pocket, a volume increasing / decreasing means capable of increasing / decreasing the volume of the recess, a displacement measuring means for measuring a relative displacement between the moving body and the static pressure pocket, and the displacement measurement. Control means for calculating an increase / decrease amount of the volume increasing / decreasing means according to a displacement amount measured by the means and outputting an operation command; and a driving means for driving the volume increasing / decreasing means based on the operation command of the control means, When the moving body approaches the pocket, the volume of the recess on the approaching side is decreased, and when the moving body moves away from the pocket, the volume of the recess on the leaving side is increased.

  According to a second aspect of the invention, there is provided a main shaft on which the moving body rotates in the first aspect of the invention, wherein the static pressure pocket, the volume increasing / decreasing means, and the relative relationship between the main shaft and the static pressure pocket. The displacement measuring means for measuring the displacement is arranged in a cylindrical shape on the outer periphery of the main shaft.

  The invention according to claim 3 is characterized in that, in the invention according to claim 2, a plurality of the volume increasing / decreasing means and the displacement measuring means are provided, respectively, and the control means is based on a displacement amount of the plurality of displacement measuring means. The volume increasing / decreasing amount of the plurality of volume increasing / decreasing means is calculated and an operation command is output.

  A feature of the invention according to claim 4 is that, in the invention according to any one of claims 1 to 3, the volume increasing / decreasing means includes a piston and a piezoelectric element that drives the piston.

  According to the invention of claim 1, when a disturbance force acts on the moving body, the relative displacement between the moving body and the static pressure pocket is measured by the displacement measuring means, and the measured displacement amount is sent to the control device. The control means calculates the volume increase / decrease amount of the volume increase / decrease means from the displacement amount and outputs an operation command to the volume increase / decrease means. When disturbance force acts on the moving body and the moving body approaches the pocket, a command to reduce the volume of the recess is issued to the volume increasing / decreasing means on the approaching side, and the recess volume decreases and the amount of oil spill from the corresponding pocket increases. To do. Since the pocket internal pressure is constant and the amount of oil outflow from the pocket increases, the gap between the moving body and the land increases. That is, the moving body moves away from the pocket. On the other hand, when a disturbance force acts on the moving body and the moving body leaves the pocket, a command to increase the recess volume is issued to the volume increasing / decreasing means on the far side, and the recess volume increases to increase the oil spill amount from the corresponding pocket. Decrease. Since the pocket internal pressure is constant and the amount of oil outflow from the pocket decreases, the gap between the moving body and the land decreases. That is, the moving body moves in a direction approaching the pocket. As described above, the disturbance displacement of the moving body is suppressed by applying the volume increasing / decreasing means in a direction that cancels the displacement of the moving body due to the disturbance force. High-speed disturbance force compared to the conventional externally supplied pressure control method that restricts the flow rate by the throttle, which has high responsiveness and high control accuracy because the recess volume is controlled by directly increasing and decreasing the recess volume in the static pressure pocket. It is possible to suppress a decrease in accuracy of the moving body with high accuracy even with fluctuations.

  According to the second aspect of the present invention, the moving body is a rotating shaft, and a static pressure pocket is arranged in a cylindrical shape on the outer periphery of the rotating shaft, thereby suppressing deterioration in accuracy of the rotating bearing that is often used at high speed rotation. can do.

  According to the invention of claim 3, since the control means can calculate using the plurality of displacement amounts measured by the plurality of displacement measurement means, the displacement direction and the displacement amount can be determined, and the volume increase / decrease of the plurality of volume increase / decrease means. Since a predetermined amount can be corrected in any direction by the combination of the above, it is possible to suppress a decrease in bearing accuracy against disturbance force fluctuations from any direction on the circumference.

According to the invention of claim 4, since the volume increasing / decreasing means is constituted by a piston, the degree of freedom of operation is large, and since it is driven by a piezoelectric element, high speed operation is possible and the volume increase / decrease of high speed operation with a wide adaptive range. The means can be made compact.

It is the schematic which shows the whole structure of the static pressure bearing apparatus of this embodiment. It is a cross-sectional detail drawing which shows the structure of the static pressure pocket part of this embodiment. FIG. 3 is a detailed view taken from the direction of the arrow A in FIG. 2 showing the configuration of the static pressure pocket portion of the present embodiment. It is the schematic which shows the whole structure of a prior art.

Hereinafter, as an embodiment of the fluid holding device of the present invention, a static pressure bearing will be described as an example with reference to FIGS.
As shown in FIG. 1, the hydrostatic bearing device 1 according to the present embodiment is rotatable by hydrostatic bearings 4 and 5 in which a main shaft 3 (moving body in the present invention) holding a tool 2 is held by a bearing housing 6. And is driven by the rotary motor 15. The hydrostatic bearings 4 and 5 are supplied with pressure oil of a predetermined pressure by the pump 13 and the pressure control valve 14. Furthermore, displacement sensors 9 and 10 that measure relative displacement between the main shaft 3 and the static pressure bearings 4 and 5, a control device 11 that outputs a displacement command based on the amount of displacement of the displacement sensors 9 and 10, and a displacement command of the control device 11 The piezoelectric element driver 12 for driving the volume increasing / decreasing means 7 and 8 is provided.

Since the hydrostatic bearing 4 has the same structure as the hydrostatic bearing 5, the details of the hydrostatic bearing 4 will be described below with reference to FIGS.
The static pressure bearing 4 includes static pressure pockets 20a to 20d including a plurality of lands 42a to 42d and recesses 41a to 41d. The lands 42a to 42d are convex portions provided on the entire outer periphery of the pockets 20a to 20d, and the recesses 41a to 41d are concave portions surrounded by the lands 42a to 42d. Pressure oil supply pipes 19a to 19d for supplying pressure oil from the pressure control valve 14 are connected to the recesses 41a to 41d. In the vicinity of the pockets 20a to 20d of the pressure oil supply pipes 19a to 19d, A diaphragm is provided. Volume increasing / decreasing means 7a and 7b are provided on the recess bottom surfaces of the pockets 20a and 20b. An oil discharge groove 21 is formed on the outer periphery of the pockets 20a to 20d, and the oil discharge groove 21 is disposed at a relative angle of approximately 90 degrees for measuring the relative displacement between the main shaft 3 and the hydrostatic bearing 4. Displacement sensors 9a and 9b are attached. Here, the relative angle of the displacement sensor arrangement is not limited to 90 degrees, and may be any angle other than 180 degrees.

  The volume increasing / decreasing means 7a for increasing / decreasing the volume of the recess forms a radial hole from the outer periphery of the static pressure bearing 4 to the recess 41a, and fixes the piezoelectric element driving portion 72a to the outer peripheral side mouth of the static pressure bearing 4 in this hole. The piston 71a sealed with the seal 73a is joined to the hydrostatic bearing 4 in a slidable manner. The volume increasing / decreasing means 7b has the same structure as the volume increasing / decreasing means 7a.

The operation of the static pressure bearings 4 and 5 configured as described above will be described.
During normal use, the pressure oil from the pump 13 is held at a predetermined pressure by the pressure control valve 14, and is supplied to the recesses 41a to 41d via the pressure oil supply pipes 19a to 19d provided with throttles. The oil in the recesses 41 a to 41 d flows out from the gap between the lands 42 a to 42 d and the main shaft 3. The main shaft 3 is held at a predetermined position by a pocket internal pressure in which the inflow oil amount from the pressure oil supply pipes 19a to 19d and the outflow oil amount from the gaps between the lands 42a to 42d and the main shaft 3 are balanced.

The principle of suppressing a decrease in bearing accuracy when disturbance force F0 such as machining load fluctuation or external vibration transmission acts on the main shaft 3 will be described below.
When a disturbance force in the pocket 20b direction acts on the main shaft 3, the main shaft 3 is displaced in the pocket 20b direction, the gap between the land 42b of the pocket 20b and the bearing 3 is reduced by the amount corresponding to the displacement, and the amount of oil outflow from the pocket 20b is reduced. Since the pressure decreases, the pressure in the pocket 20b increases. On the other hand, in the pocket 20d at a position facing the pocket 20b, the gap between the land 42d and the main shaft 3 increases corresponding to the displacement, and the pressure in the pocket 20d decreases. As a result, the main shaft 3 is balanced by the land clearance where the sum of the increased holding force F1 due to the pressure increase of the pocket 20b and the decreased holding force F2 due to the pressure decrease of the pocket 20d becomes equal to the disturbance force F0. Here, when the piston 71b of the volume increasing / decreasing means 7b is advanced, the volume of the recess 41b is decreased, and the amount of oil flowing out of the pocket 20b is increased. Since the oil pressure in the pocket 20b is constant, the gap between the land 42b and the main shaft 3 increases, that is, the main shaft 3 is pushed back, and the displacement of the main shaft 3 due to disturbance force is reduced.

  On the contrary, when a disturbance force in the pocket 20d direction acts on the main shaft 3, the main shaft 3 is displaced in the pocket 20d direction, and the gap between the land 42b of the pocket 20b and the main shaft 3 increases by the amount corresponding to the displacement. Here, when the piston 71b of the volume increasing / decreasing means 7b is retracted, the volume of the recess 41b increases and the amount of oil flowing out of the pocket 20b decreases. Since the oil outflow amount in the pocket 20b is reduced while the oil pressure in the pocket 20b is kept constant, the gap between the land 42b and the main shaft 3 is reduced. 3 is reduced.

  In the volume increasing / decreasing means 7a and 7b, the forward and backward advancement of the pistons 71a and 71b is performed by the forward and backward advancement of the piezoelectric element driving units 72a and 72b based on a command from the piezoelectric element driver 12.

Below, the effect | action which suppresses the fall of the spindle precision by disturbance force is demonstrated concretely.
When the main shaft 3 is displaced by a disturbance force, the displacement is measured by the displacement sensors 9a and 9b. The measured displacement amount is transferred to the control device 11, and the displacement amounts of the main shaft 3 and the displacement direction are calculated by synthesizing the displacement amounts by the control device 11. The calculated displacement of the main shaft 3 is decomposed and converted into the radial displacement of the circumferential center positions of the pockets 20a and 20b, thereby obtaining the displacement of the main shaft 3 with respect to the pocket 20a and the displacement of the main shaft 3 with respect to the pocket 20b. Next, the volume increase / decrease amount of the volume increasing / decreasing means 7a that minimizes the displacement of the main shaft 3 with respect to the pocket 20a is calculated, and the command value of the feed amount of the piston 71a of the volume increasing / decreasing means 7a is determined. Similarly, the command value for the feed amount of the piston 71b is determined for the pocket 20b.

Based on the command value of the feed amount of the piston 71a calculated by the control device 11, the piezoelectric element driving unit 72a is driven via the piezoelectric element driver 12, and the piston 71a of the pocket 20a moves forward and backward, and the main shaft 3 in the pocket 20a direction. Suppresses displacement. Similarly, in the pocket 20b, the displacement of the main shaft 3 in the pocket 20b direction is suppressed.
As a result, the displacement caused by the disturbance force of the main shaft 3 with respect to the static pressure bearing 4 can be suppressed, and the same control is performed on the static pressure bearing 5 to suppress the displacement caused by the disturbance force. By minimizing the main shaft displacement caused by the disturbance force in the hydrostatic bearings 4 and 5, the accuracy of the bearing is reduced due to the disturbance force in the translation of the two shafts excluding the axial direction of the main shaft 3 and the pitching and yawing of the main shaft 3. Can be suppressed.

  According to the above structure, the volume of the pockets 20a, 20b is directly increased / decreased by moving the pistons 71a, 71b back and forth to suppress disturbance displacement of the main shaft 3, so that the flow rate by the throttle as in the conventional external supply pressure control system is reduced. There is no response delay due to restrictions. Therefore, it is possible to suppress spindle displacement with high accuracy following high-speed disturbance force fluctuations compared to the conventional technology, and it is possible to suppress deterioration in bearing accuracy even when high-frequency vibrations or high-speed fluctuations in machining force occur, and high accuracy and high speed. Processing can be realized.

The displacement due to the disturbance force of the main shaft 3 is measured by the two displacement sensors 9a and 9b to measure the displacement amount and the direction of the main shaft 3, and the circumferential center positions of the pockets 20a and 20b provided with the volume increasing / decreasing means. Since the displacement suppression control of the pockets 20a, 20b is performed in terms of the radial displacement of the bearing, it is possible to suppress a decrease in bearing accuracy against disturbance force fluctuations from any direction on the circumference.
Since the volume increasing / decreasing means 7a, 7b is constituted by a piston, the degree of freedom of operation is large, and since it is driven by a piezoelectric element, high speed operation is possible, and a high speed operating volume increasing / decreasing means having a wide adaptive range can be configured compactly.

<Deformation of this embodiment>
The above embodiment has been described with respect to the rotary hydrostatic bearing. However, the present invention is not limited to this, and can be applied to a hydrostatic guide in which the main shaft 3 is a translational motion body and static pressure pockets are arranged in a plane. .
A high-pass filter may be added to the outputs of the displacement sensors 9 and 10 so that only the high frequency component of the disturbance force is suppressed by the volume increasing / decreasing means 7 and 8. (In this case, the low frequency component of the disturbance force is suppressed by the centripetal action of the original static pressure bearing)
Further, the piezoelectric element driving units 72a and 72b may be replaced with other driving means such as an electromagnetic solenoid or a motor.
In the above-described embodiment, the pistons 71a and 71b moving to the volume increasing / decreasing means 7 and 8 are used. However, by making the recess wall surface elastically deformable (for example, thinning or diaphragm), the volume of the recesses 41a and 41b can be reduced. You may comprise so that it may increase / decrease.
For example, when the direction of the displacement due to the disturbance force can be limited to a specific direction as in the case where the static pressure bearings 4 and 5 are used for the grindstone shaft, the displacement sensors 9 and 10 detect the displacement in that direction. A configuration with only one set is possible.
Similarly, when the direction in which the displacement due to the disturbance force can be suppressed can be limited to a specific direction, the volume increasing / decreasing means 7 and 8 may be configured to have only one set in the recess located in that direction.

1: Static pressure bearing device 3: Main shaft 7, 8: Volume increasing / decreasing means 9, 10: Displacement sensor 11: Control device 12: Piezoelectric element driver 13: Pump 14: Pressure control valve 20a-20d: Static pressure pockets 72a, 72b: Piezoelectric element driving units 41a to 41d: recesses 42a to 42d: lands

Claims (4)

  A static pressure pocket comprising a recess and a land provided around the recess, a pressure oil supply means for supplying pressure oil to the recess, a movable body supported by the pressure oil in the static pressure pocket, and the recess A volume increasing / decreasing means capable of increasing / decreasing the volume of the moving body, a displacement measuring means for measuring a relative displacement between the movable body and the static pressure pocket, and calculating an increase / decrease amount of the volume increasing / decreasing means according to a displacement amount measured by the displacement measuring means. Control means for outputting an operation command, and drive means for driving the volume increasing / decreasing means based on the operation command of the control means, and when the movable body approaches the pocket, the volume of the recess on the approaching side is set. The fluid holding device, wherein the volume of the recess on the side of the moving body is increased when the moving body moves away from the pocket.   A main shaft on which the movable body rotates, and the static pressure pocket, the volume increasing / decreasing means, and a displacement measuring means for measuring relative displacement between the main shaft and the static pressure pocket are formed in a cylindrical shape on the outer periphery of the main shaft. The fluid holding device according to claim 1, wherein the fluid holding device is arranged.   A plurality of the volume increasing / decreasing means and the displacement measuring means are provided, and the control means calculates an increase / decrease amount of the plurality of volume increasing / decreasing means from a displacement amount of the plurality of displacement measuring means and outputs an operation command. The fluid holding device according to claim 2.   The fluid holding apparatus according to claim 1, wherein the volume increasing / decreasing means includes a piston and a piezoelectric element that drives the piston.

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